The present invention is related to WDM (Wavelength Division Multiplexing) optical systems and, more particularly, to systems and methods for adding and dropping WDM communication channels in WDM systems.
In WDM systems, multiple optical signals having different wavelengths share an optical fiber, each wavelength defining a particular communication channel. This technique has many advantages in implementing optical communication systems including increased capacity and the ability to use passive optical components to redirect a portion of the data flowing along the fiber for processing at an intermediate node.
A representative WDM system may include multiple nodes connected to one another by optical fiber. For example, the nodes may be connected in a ring. Each node typically uses only certain wavelengths (also referred to herein as WDM channels) for transmission and reception and leaves the other wavelengths untouched. A WDM add/drop multiplexer isolates and removes (or “drops”) these channels from the light flow past the optical fiber node. The channels that are dropped in this way are processed by receiver circuitry within the node or otherwise rerouted. The node also generates signals on these channels for transmission onto the fiber. The add/drop multiplexer combines (or “adds”) these new signals into the light flow past the node. Hence the add/drop multiplexer implements the drop and add functions of the node, which itself is often termed an add/drop node on the optical fiber.
But there are many challenges in implementing add-drop multiplexers, in particular, configurable add/drop multiplexers by which the WDM channels which are added or dropped, or both, may be dynamically changed. These challenges are exacerbated by the increasing use of DWDM (dense wave division multiplexing) where the WDM channels are very closely spaced in the frequency (or wavelength) domain. For example, the spacing between wavelength components may be 25 GHz or less making frequency-selective processing of the optical signal difficult with passive optical components of reasonable cost.
The present invention addresses at least some of these challenges with an reconfigurable add/drop multiplexer which has maximum optical performance with functional flexibility at relatively low cost.